Chapter 7. How Cells Release Chemical energy

Transcription

1 Chapter 7 How Cells Release Chemical energy

2 Overview of Carbohydrate Breakdown Pathway Plants and all other photoautotrophs get energy from the sun, heterotrophs get by eating plants and one another ATP is a common energy currency that drives metabolic reactions in cells

3 Pathways of Carbohydrate Breakdown Starts with glycolysis in the cytoplasm Convert glucose and other sugars to pyruvate

4 Comparison of main pathways Fermentation pathway Produces ATP under anaerobic conditions Ends in cytoplasm, do not use oxygen, yields 2 ATP per molecule of glucose Aerobic Respiration Produces ATP by using oxygen Ends in mitochondria, uses oxygen, yields up to 36 ATP per glucose molecule Oxygen acts as the final acceptor of electrons used during these reactions

8 Glycolysis Glucose Breakdown Starts First step Conversion of glucose to pyruvate Enzymes of glycolysis use two ATP to convert one molecule of glucose to two molecules of three-carbon pyruvate Reactions transfer electrons and hydrogen atoms to two NAD + (reduces to NADH) 2 ATP is formed by substrate-level phosphorylation

12 Second Stage of Aerobic Respiration Krebs Cycle Break down of pyruvate to Carbon dioxide The second stage of aerobic respiration takes place in the inner compartment of mitochondria It starts with acetyl-coa formation and proceeds through the Krebs cycle

13 outer membrane (next to cytoplasm) inner membrane glucose (glycolysis) 2 pyruvate OUTER COMPARTMENT inner mitochondrial compartment outer mitochondrial compartment (in between the two membranes) CO2 INNER COMPARTMENT 2 acetyl CoA ATP Breakdown of 2 pyruvate to 6CO2 yields 2 ATP. Also, 10 NADH Krebs coenzymes are reduced (8 Cycle FADH 2 NADH, 2 FADH2). The coenzymes carry hydrogen ions and electrons to sites of the third stage of aerobic respiration. a An inner membrane divides a mitochondrion s interior into two compartments. The second and third stages of aerobic respiration take place at this membrane. b The second stage starts after membrane proteins transport pyruvate from the cytoplasm, across both mitochondrial membranes, to the inner compartment. Six carbon atoms enter these reactions (in two pyruvate), and six leave (in six CO2). Many coenzymes form.

14 Acetyl-CoA Formation Two pyruvates from glycolysis are converted to two acetyl-coa Two CO 2 leave the cell Acetyl-CoA enters the Krebs cycle

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16 Krebs Cycle In each turn of the Krebs cycle, one acetyl- CoA is converted to two molecules of CO 2 After two cycles Two pyruvates are dismantled Glucose molecule that entered glycolysis is fully broken down

17 Energy Products Reactions transfer electrons and hydrogen atoms to NAD + and FAD Reduced to NADH and FADH 2 ATP forms by substrate-level phosphorylation Direct transfer of a phosphate group from a reaction intermediate to ADP

18 Net Results Second stage of aerobic respiration results in Six CO 2, two ATP, eight NADH, and two FADH 2 for every two pyruvates Adding the yield from glycolysis, the total is Twelve reduced coenzymes and four ATP for each glucose molecule Coenzymes deliver electrons and hydrogen to the third stage of reaction

25 Anaerobic Energy-Releasing Pathways Fermentation Pathway Begins with glycolysis and ends in the cytoplasm Do not use oxygen or electron transfer chains Two ATP is formed from glycolysis Final steps do not produce ATP; only regenerate oxidized NAD + required for glycolysis to continue

28 Alcoholic fermentation Role of Yeast in fermentation They are unicellular fungi Sacchromyces cerevisiae (Baker s s yeast) Cells release carbon dioxide in fementation and dough expands Other strains are used in the production of wine

32 The Twitchers Slow-twitch and fast-twitch twitch skeletal muscle fibers can support different activity levels Aerobic respiration and lactate fermentation proceed in different fibers of muscles These pathways yeilds ATP for muscles

33 Alternative Energy Sources Complex Carbohydrate break down They are broken down into simple sugars like glucose Glucose gets converted to glucose-6-phosphate. If the body doesn t t need glucose for energy,glucose-6-phosphate can be converted to glycogen for storage When blood sugar drops, glycogen is converted to glucose-6-phosphate and and enters the glycolysis pathway

34 Alternative Energy Sources; Energy from Fats Most fat in the body are triglycerides Enzymes convert fat into glycerol and fatty acid Glycerol is converted into PGAL, an intermediate of glycolysis The carbon back bones of the fatty acid tail is broken apart, and fragments are converted into acetyl CoA, which can enter the Krebs cycle

35 Energy from Proteins Enzymes split proteins into amino acid subunits The amino group is removed and becomes ammonia, then urea Urea is excreted Carbon Back bones can enter at several different points of Krebs cycle

37 Life s s Unity Photosynthesis and aerobic respiration are interconnected on a global scale In its organization, diversity, and continuity through generations, life shows unity at the bioenergetic and molecular levels

38 sunlight energy in Photosynthesis Driven by energy input from the sun, electrons and hydrogen are used to form ATP. ATP energy drives the synthesis of glucose from hydrogen, electrons (delivered by coenzymes), and carbon dioxide s atoms. glucose (stored chemical energy) carbon dioxide, water oxygen Aerobic Respiration Energy input from two ATP initiates three stages of reactions. Many ATP form during thecomplete breakdown of glucose to carbon dioxide and water. chemical energy in many ATP available to drive nearly all cellular tasks energy out (heat) energy out (heat)

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